Various types of wheel speed transducers are known which provide pulses, the frequency of which is representative of the speed of a rotating element. When analyzed with respect to standard time intervals, or time norms, the speed can be calculated as the average pulse rate with respect to a predetermined timing interval. This system, thus, is effectively a counting system with respect to recurring time periods. Transducers which provide such output signals, typically, are inductive transducers which are fixed on a body of a vehicle, and magnetically influenced by star wheels gears, or other toothed elements coupled to a rotating elment of the vehicle, for example, to a vehicle wheel. Rough operating conditions which are found in actual practice, for example in automotive vehicles, require high performance, highly reliable transducers, and, thus, for automotive use, inductive transducers are used exclusively. Such inductive transducers have a fixed sensor and a transducer wheel. Current speed measuring systems, for example for anti-brake lock systems (ABS), use a gear wheel as the transducer or star wheel, having symmetrical teeth. The fixed transducer element is a coil with a permanent magnet. The magnet, coil and star wheel form a magnetic loop, the magnetic resistance or reluctance of which changes as the angle of the wheel, with respect to the fixed transducers, changes, that is, during the transition between teeth and gaps between the teeth. The resulting change in magnetic flux induces an alternating voltage wave in the coil which has a voltage proportional to the speed of the change of magnetic flux, and which, if the teeth are effectively square, will have an approximately sinusoidal wave form. The amplitude of the sensor voltage is dependent on the speed of the star wheel as well as the distance between the wheel and the transducer pick-up or coil element.
In various measuring methods to determine the speed of such a wheel, the zero-crossover of the signal is used to determine the vehicle wheel speed. If the vehicle wheel, and hence the star wheel, turns very slowly, that is, at low speeds, the distance of sequential changes in polarity of the signal--with respect to time--is long, and the wave shape will be shallow. It is difficult to evaluate such signals.